1. Field of the Invention
The present invention pertains to the aqueous processing of various articles, including the immersion cleaning of semiconductor wafers, using deoxygenated aqueous rinse solutions.
2. Description of the Related Art
As will be seen herein, the present invention is directed to the aqueous treatment of a wide variety of commercially important articles, such as liquid crystal displays, flat panel displays, memory storage disk substrates, as well as photographic plates and film. The present invention has found immediate commercial acceptance in the field of semiconductor wafers, especially wafers of a type which are ultimately divided to form a plurality of electronic devices.
During the course of producing commercial semiconductor wafers, layers of various materials are built up on one surface of a wafer blank. These various layers are processed using several different etching techniques, each of which results in a residue which impairs further device fabrication. It is important that such residues be effectively removed. Typically, the several types of residue are removed with solvents especially adapted for the particular residues. While such solvents are generally effective for removing residues, solvents remaining on the surfaces of the semiconductor device also impair further device fabrication steps.
Accordingly, it is important that the solvents be removed from the semiconductor device and it is known that water rinsing is an efficient means of solvent removal. However, semiconductor device layer materials have changed over the years, and presently semiconductor device manufacturers are employing materials which are subject to corrosion upon contact with water. In an effort to reduce the corrosion problem, carbon dioxide gas has been sparged, i.e., bubbled, into the rinse water to partially lower the pH of the rinse water. However, bubbling carbon dioxide into water rinses used in the semiconductor device fabrication industry has proven to be only marginally successful in reducing the extent of corrosion, and further adds the risk of introducing contaminating particles into solution. In an effort to overcome growing problems of corrosion, the semiconductor device fabrication industry has investigated intermediate rinse steps using non-aqueous rinse solutions. However, such non-aqueous solutions have proven to be less effective than rinse water in removing solvents and wafers are still routinely rinsed with water, despite the corrosion effects.
Significant efforts have been expended in reducing the amount of exposure of a wafer containing alloys of copper and aluminum to rinse water. However, it appears that, in order to meet future requirements for improved electrical performance, the aluminum content of the alloy must be substantially reduced and possibly eliminated, thus substantially increasing the susceptibility of the wafer layer materials to corrosion, at higher levels than those presently experienced.
One example of efforts to improve wafer production involves oxygen removal to reduce oxide growth on the surface of semiconductor wafers. For example, literature describing the PALL SEPAREL Model EFM-530 Degasification Module addresses the reduction of dissolved oxygen in deionized water, in a manner which avoids potential defects to semiconductor devices caused by the formation of unwanted oxide layers. As is known in the art, an oxide layer forms when pure silicon is exposed to an oxygen source, such as dissolved oxygen in a rinse water or other aqueous medium. The oxide layer can change the surface of the silicon from hydrophobic to hydrophilic, a condition which is undesirable in some aspects of wafer processing, such as pre-diffusion cleaning operations. Accordingly, the PALL Degasification Module addresses the need to deoxygenate rinse water to avoid formation of a silicon dioxide layer in the rinse after the wafer is treated with an HF etch solution. As can be seen, the problem addressed by the PALL Degasification Module is not related to problems encountered in controlling corrosion of aluminum, such as pitting and etching, as has been experienced in processing wafers carrying copper/aluminum structures on their surface. While dissolved oxygen is also objectionable from a corrosion standpoint, the corrosion problem is not concerned with the formation of unwanted oxides. A further, more complete system control over wafer processing so as to reduce corrosion in wafers containing copper/aluminum structures is needed.
It is an object of the present invention to provide cleaning for semiconductor wafers using aqueous solutions which are treated in a manner to eliminate corrosion of semiconductor device materials layered on semiconductor substrates.
Another object of the present invention is to provide cleaning of the above-described type which is effective even in relatively small, hollow structures formed in a semiconductor surface, such as vias.
A further object of the present invention is to provide aqueous treatment of the type described above which removes dissolved oxygen from an aqueous solution while controlling the pH of the aqueous solution.
Another object of the present invention is to provide arrangements for aqueous treatment of many different types of devices using conventional readily obtained equipment, and consumables which are relatively inexpensive.
Yet another object of the present invention is to provide process arrangements of the type described above by employing an osmotic membrane degasifier and using a carrier fluid (preferably a gas) comprised of one or more components, preferably for oxygen removal and, optionally, pH control or other chemical adjustment to the aqueous solutions.
These and other objects according to principles of the present invention are provided in apparatus for processing a workpiece, comprising:
a cleaning chamber defining a cavity for receiving the workpiece and a device opening through which said workpiece is passed into and out of the cavity;
an osmotic membrane degasifier defining a degasifier cavity, a membrane dividing the degasifier cavity into first and second parts, a aqueous solution inlet and a aqueous solution outlet associated with said first part to direct aqueous solution into contact with one side of the membrane, and a carrier gas inlet and a carrier gas outlet associated with said second part to direct carrier gas into contact with the other side of the membrane;
and the aqueous solution outlet coupled to the cleaning chamber.